1. Field of the Invention
This invention is related to the growth of semiconductor devices on non-polar III-nitride films, more specifically, LEDs (light emitting diodes), LDs (laser diodes), VCSELs (vertical cavity surface emitting lasers), RCLEDs (resonant cavity LEDs), and MCLEDs (micro-cavity LEDs).
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification as indicated by the citation within brackets, i.e., [REF x], wherein x is a number. A list of these different publications identified by the number x can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Conventional III-nitride optical devices, such as gallium nitride (GaN) LEDs, are grown in the c-direction of the wurtzite unit cell. A net polarization occurs from contributions of spontaneous and piezoelectric polarizations in the direction of film growth. The resulting built-in electric field causes the band structure to be slanted, most notably in the quantum wells. This has a huge impact on the behavior of c-plane GaN optical devices. The slanted quantum wells consequently diminish the spatial overlap of the hole and electron wavefunctions, in turn decreasing radiative recombination efficiency. In addition, the emission wavelength decreases (blue shift) with increasing drive current as explained by the Quantum Confined Stark Effect (QCSE) [REF 1].
M-plane and a-plane GaN are defined as non-polar GaN because there is no net polarization field normal to those respective planes. Therefore, the band structure is not slanted like c-plane, which means quantum well structures on these planes have flat bands. Radiative efficiencies are theoretically higher, and no wavelength shift occurs. There have been recent reports of non-polar LEDs [REF 2, 3]. However, the output powers and efficiencies are well below that of c-plane LEDs. The main reason for this poor performance is commonly attributed to high dislocation densities.
Current non-polar GaN optical devices have not achieved the performance standards necessary for bringing them to market. The highest power m-plane LED reported is 1.79 mW at 20 mA [REF 3], and there has been no report of an electrically pumped LD grown on m-plane GaN. Optical devices grown on m-plane GaN have the benefit of emitting polarized light [REF 4]. This lends them well to the application of backlighting for displays, especially LCDs (liquid crystal displays), since a light polarizer would not be required.
Thus, there is a need in the art for improved methods of fabricating of high performance non-polar III-nitride optical devices. The present invention satisfies this need.